Color television system



May 12, 1953 J. EVANS COLOR TELEVISION SYSTEM 5 Sheets-Sheet l Filed Jan. 24, 1950 INVENTOR l mi' will f TTORNEY J. I EVANS 2,638,499

3 Sheets-Sheet 2 COLOR TELEVISION SYSTEM May L2,

Filed Jan. 24, 1950 May i2, w53 J. EVANS COLOR TELEVISION SYSTEM 5 Sheets-Sheet 3 Filed Jan. 24, 1950 v T S S E3 NALE Q E NmvvUl-XJNS w U INVENTOR Patented May l2, 1953 COLOR TELEVISION SYSTEM John Evans, Blawenburg, N. J., assignor to Radio Corporation of America, a corporation of Dela- Ware Application January 24, 1950, Serial No. 140,223

16 Claims.

This invention relates to color television system and particularly, but not necessarily exclusively, to color :filter devices employed in such systems.

One of the systems for reproducing by television methods images substantially in their natural colors which, in theory at least, is relatively simple is that type of system in which the different color components of the image to be reproduced are displayed as black and White partial images and which are viewed or projected through a succession of differently colored light iilters. The color filters which previously have been employed have been ones which require mechanical movement whereby to successively interpose in the light path filter sections having respectively the properties of transmitting differently colored light. Filter devices of this character have required a driving mechanism which has the disadvantage of producing noise and Vibration. Such disadvantages may .be overcome by employing a color lter of the type embodied in this invention.

Furthermore, a mechanically movable iilter device has a deiinite speed limitation by reason of which it has not been possible to display the successive partial color television images in sufficiently rapid succession to overcome completely a perceptible color flicker.

Moreover, because of the speed limitations of a filter device of the mechanically movable type, it is necessary that the image be reproduced in complete fields or frames of the diiierent color components thereof. Consequently, the color changes are not eiTected rapidly enough to completely eliminate color fringes when the subject matter of the image comprises relatively fast action such as that occurring in certain types of athletic contests, for example, where balls or other objects are caused to move at relatively high rates of speed or in performances such as juggling acts, to cite but a few typical examples. Mechanically movable color iilters of the prior art are obviously not susceptible of operation at frequencies of the order of the elemental picture dot frequencies. Therefore, they may not be utilized in systems such as the so-called dot multiplex color television system covered by a copending United States application of John Evans, Serial No. 111,384, led August 20, 1949 and entitled Color Television. Such a system is substantially free from many of the inherent limitations such as color fringing of other types of prior art systems.

Accordingly, it is an object of the present 2 invention to provide an improved color television system embodying colored light lter devices requiring no mechanical movement thereof.

Another object of the invention is to provide an improved color television system embodying a colored light filter which is operable at field or frame frequencies, at horizontal line frequencies or even at elemental picture dot frequencies.

Still another object of the invention is to provide an improved color lter device for use in color television systems and which is operated entirely electrically and has no moving parts.

A further object of the invention is to provide an improved color filter embodying a plurality of fixed or stationary color filter elements and employing an electrically controlled optical system to vary the direction of the light path through the device.

A still further object of the invention is to provide an improved color filter device for use in a color television system which employs the optical properties of standing Waves in a transparent medium to selectively direct light through a multiplicity of differently colored light transmitting sections.

According to the invention, there is provided an improved color television system embodying at both the transmitter and the receiver locations a novel colored light filter having no moving parts and being susceptible or operation entirely electrically. At the transmitting station or other pickup point colored light from the television subject is passed through selected sections of the filter device capable respectively of transmitting the light of predetermined colors onto the photosensitive electrode of a television image signal generating tube. The vdeo signals developed in this manner are transmitted as desired to one or more receiving stations either by space radiation or by suitable conductors and are representative of the different color components of the subject. The received video signals are employed to reproduce black and white partial images of the subject which are projected for viewing through a non-mechanical, electricallyoperated color filter device in accordance with a feature of this invention.

The color filter device in accordance with this invention includes a stationary translucent area which is sub-divided into a multiplicity of sections capable, respectively, of transmitting differently colored light. ll'here also is provided, in spaced relationship to the translucent color area, a transparent section which receives White light from the image reproducing device. The space between the translucent and transparent sections of the color filter device includes a transparent medium in which there may be produced standing pressure Waves which have the optical property of focussing the incident light onto correspondingly colored components of the tranelucent section. In one illustrative embodiment oi the invention, the color iilter device also includes an electromechanical vibratory member which, when suitably energized, produces pressure waves in the transparent medium. The device also includes a highly reflecting wall from which the pressure Waves may be reflected to form standing Waves in the medium. By means of a pair of additional electromechanical vibratory devices, the standing waves may be shifted laterally in the medium so as to selectively direct the incident light onto a succession of different color transmitting sections of the translucent area.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method oi operation, as well as additional objects and advantages thereof, will best be understood from the following description taken in connection with the accompanying drawing, in which:

Figure l is a diagrammatic representation oi a video signal generating apparatus according to the invention and embodying a color filter device in accordance With the invention;

Figure 2 is a similar diagrammatic circuit structure of an image reproducing system in accordance with the invention;

Figures 3 and 4 are horizontal sectional and front elevational views respectively of a color nlter device embodying the invention;

Figures 5, 6, and 'l are fragmentary diagrammatic representations showing the operation of the color lter device in accordance with the invention;

Figur 8 is a circuit diagram of one means of developing the necessary control voltages for operation of the color filter devices in accordance with the invention;

Figure 9 is a series of curves representing wai.- .torins o1 voltages developed at diiierent points of the circuits of Figures 8 and 10 for reference in explaining the operation oi these voltage developing circuits; and,

Figure lll is another circuit diagram of typical apparatus by means of which the voltages developcd by means of apparatus such as that shown in Figure 8 may be combined tc develop one control voltage for operation or the color 'Filter device according to this invention.

Having reference rst to Figure 1 of the drawings, there is shown in block diagram form the major essential components of a television transmitting apparatus embodying the present invention. The television subject which is represented by an arrow 2l is illuminated in the usual manner and the light reiiected therefrom is projected through a color flier device 22 constructed in accordance with the present invention and the particle component color images of the subject are further projected by means of a suitable optical system represented at 23 upon the photosensitive electrode 24 of a television pickup or camera tube 25. The particular type oi camera tube employed is immaterial, it merely being necessary to systematically analyze the optical image of the television subject to develop at an output electrode 26 a train of video signals representative respectively of the different component colors of the subject.

The analysis of the optical image pr jected upon the electrode 2li is effected under the control of a deflection system represented by the yoke 2l, the particular form of which will depend, in some measure, upon the type of camera tube employed. The deiiection system is operated by the impression thereon of suitable energy derived from deflection control circuits 28.

The video signals generated at the output electrode 26 are amplified by a video signal amplifier 29 and are impressed upon a transmitter 3l ior suitable modulation of a carrier Wav Also, system control signals derived from the deflection control circuits 2t are impressed upon the transmitter 3i for suitable mixing with the video signals to form a composite television system for radiation by means of an antenna 312.

The color filter 22, in accordance with this invention, requires excitation for the purpose of producing the standing Waves by means of which to effect color selection. In. this form of the invention, the medium in which the standing Waves are to be produced is excited by means of a sinusoidal voltage such as repre-sented at 33 which may be derived from a source of excitation voltage 3:1. In order to variably position the standing Waves Within the transparent medium of the color filter 22, there are employed two oppositelyphased voltages having stepped waveforms such as represented at iii and SG, both of which may be derived irom a source ci keying voltages 37. In order that the color selecting voltages 35 and 35 be properly related in time to the video signals devolo eed by the camera tube 25, the source of keying voltages 3l is controlled by a keying frequency oscillator 538 Which synchronized from the deflection control circuits 28 to produce a sine v/ave voltage such as that represented at 3S) having a frequency equal to or harmcnically related to the frequency at which the color changes of the video signals is eiected.

In Figure 2, there is shown the major essential circuit components or" receiving apparatus reduire to reproduce, from received video signals transmitted in the manner described, an image of the television subject substantially in its natural colors. The receiving apparatus cornpris-es a carrier wave intercepting antenna lll to Jhich is coupled the usual television receiver 32. It will be understood that the receiver i2 may include apparatus such as one or more stages of radio frequency signal amplification, a frequency converted or rst detector, one or more stages of intermediate frequency signal ampliiication and a signal or second detector. Accor ingly, it will be understood that the signals derived from the television receiver l2 are composite television signals including 'the video signal component and the system control signals, such as the horizontal and vertical synchronizing pulses. The output circuit of the television receiver L22 is coupled to a yvideo signal separator i3 by means o which the video signals are recovered to the exclusion of the system control signals. The video signals developed in the output circuit of the separator t3 are ampliiied by a video signal ampliuer fill and impressed upon the electron beam intensity control electrode such as a grid l5 of a monochromatic image reproducing device such as a cathode ray tube 45.

The composite television signals developed in the output circuit of the receiver l2 also are impressed upon a synchronizing signal separator 41 by means of which the system control signals such as the horizontal and vertical synchronizing pulses are recovered to the exclusion of the video signal component. The system control signals are impressed upon deection control circuits 38 by means of which there are produced scanning voltages for impression upon a deflection yoke 49 of the cathode ray tube 46, whereby to effect deection of the electron beam over the usual luminescent screen I for the reproduction of the television image. 'Ihe black and white television images reproduced upon the screen 5I are translated through a condensing lens system represented at 52 through a color iilter device 53 in accordance with this invention and nally projected by means of a projection system represented at 51% onto a viewing screen 55.

The color lter device 53 may be similar to the device 22 at the transmitting station and may be energized for the creation of standing waves when excited by a sinusoidal voltage such as that represented at 56 and derived from a source of excitation voltage 5l. Also, the control of the standing Waves in the color lter device for color selection purposes is effected under the control of oppositely-phased voltages having stepped waveforms such as represented at 58 and 59 derived from a source of keying voltages 5 l As in the transmitting apparatus, the source of keying voltages in this embodiment of the invention is controlled by a sinusoidal voltage such as represented at 62 and which may be derived from a keying frequency oscillator 63 synchronized by means of the system control signals derived from the synchronizing signal separator lll.

Aside from the details of the color filter devices used at the transmitting and receiving stations respectively and the manner in which they function to generate video signals representative of the color components of the television subject and to reproduce from such signals television images substantially in their natural colors, it is considered that the general operation of the color television system described is somewhat obvious. However, the general operation will be described briefly with particular reference to a system operating according to the dot multiplex principle such as that disclosed in the copending Evans application to which reference has been made.

In such a system, assuming a three color reproduction, each elemental area of the subject is analyzed in succession for the three color content thereof. The train of video signals generated by the camera tube 25 thus consists of three video signals representing respectively the three colors of one elemental area of the subject followed immediately by three additional video signals representing respectively the three color component of the next succeeding elemental area of the subject. In such a system, therefore, it is necessary that the color lter device, by means of which such an analysis of the subject is made, be of such a character that, during the analysis of each elemental area of the subject, it be susceptible of transmitting the light reected from the subject onto the photoelectric electrode 24 through three distinctively colored filter sections. It, therefore, is necessary that the light derived from the subject be switched at a frequency which is three times the dot or elemental area frequency. A similar requirement also is necessary at the receiving station. It is obvious that mechanically movable color filter. devices are incapable of meeting such a requirement. The transmitting apparatus of Figure 1, accordingly, functions to project light from the subject 2| onto the photoelectric cathode 24 of the camera tube 25 which is changed in color by the lter device 22 in the manner described so that as succeeding elemental areas of the electrode 24 are scanned, there are developed at the output electrode 26 video signals of the character described.

At the receiving station of Figure 2 the apparatus functions substantially in the same manner as the transmitting apparatus except, of course, that the video signals are translating into light, the color of which, when projected upon the screen 55, is varied by means of the color lter 53 to reproduce an image of the television subject substantially in its natural and original colors.

In order to more clearly understand the nature of the color lter device and its Inode of operation, reference now will be made to Figures 3 and 4 of the drawings. The color lter device consists essentially of a material which is `not only transparent but which also has substantial acoustic rigidity. There are many substances possessing both of these characteristics among Which are certain solids, such as a high grade of parain and numerous liquids such as kerosene, carbon tetrachloride, carbon disulphide, and nitrobenzol. Assume for the purpose of the present disclosure that a liquid material such as kerosene is used. It may be confined by a container such as a small rectangular hollow casing 64, the top and bottom and ends of which may be formed entirely of metal or any other suitable material. Consider that the illustration of Figure 3 is a horizontal cross sectional view of the container 64 so that, as seen in the drawing, a horizontal plane of the device is illustrated. The side wall of the container which is faced toward the kinescope is provided with a plain transparent area 65 formed, for example, of a good grade of glass or transparent plastic material. The opposite and substantially parallelly arranged wall of the container 64 also preferably has a transparent inner portion 55 which, for purposes of illustrative disclosure, will be considered as glass.

On the outer surface of the glass wall 65' is provided a plurality of translucent differently colored sections, for example, red, green, and blue light transmitting elements such as 6l, 68, and 69, respectively. In a preferred form of the invention, the color lter elements such as Sl, B8, and 69 have striated congurations as better illustrated in Figure 4. It will be noted that the color filter sections are provided in groups of three in which the same color sequence is repeated in all groups. It also is considered to be more practical to provide a multiplicity of color filter groups in order to minimize, insofar as it is considered practical to do so, the distance through which the standing waves have to be moved in order to selectively direct the light in the manner desired. The number of color filter sections that may be employed is subect to certain limitations such as the grain size of the photographic emulsion used to form the sections in accordance with a preferred embodiment of the invention, the degree of accuracy with which the standing waves may be controlled, and the like. One practical arrangement which has been successfully employed is to provide color lter striations in number equal substantially to 7 100 per inch. It should bevunderstood, however, that such a structure is disclosed herein only for illustrative purposes. Color lter striations of the order of 500 to the inch have been produced. It, however, is considered to be unnecessary to employ a lter structure of this degree of neness for ordinary purposes because, .as will be more completely explained hereinafter, the width and/or number of the color filter sections do not in any way affect the resolution or definition of the image to be reproduced. Furthermore, it is entirely practical to effect movements of the standing waves at the relatively high frequency required over distances approximately equal to lAOO of an inch.

Adjacent each of the end walls 1l an-d 12 of the container 64 and insulated therefrom as indicated at 13 and 14 is mounted a pair of substantially identical electromechanical vibratory devices such as piezolelectric quartz crystals 'l5 and 16. Also, there is mounted an exciting crystal 11 on the face of one of the pair of crystals such as 15 as shown.

The crystal 11 is excited by means of an alternating voltage such as represented by the wave 18 at a frequency which is sufciently high to produce pressure waves in the material within the container 64 corresponding to the number of color filter striations such as 61, S8, and 69. The inner or free face of the crystal 16 provides a good reflecting surface for the pressure waves generated by the crystal 11 so that a reilected pressure wave is developed in opposite phase for each of the impinging waves created by the crystal 11. As a result, a standing wave pattern such as that represented at 19 is produced. As a result of this standing wave pattern, the pressure of the material within the container 64 varies substantially in accordance with the waveform of the voltage 13 by which the crystal 11 is excited. While not necessarily limited thereto a sinusoidal excitation of the crystal 11 is disclosed so that the pressure variation in the optical material also will have a sinusoidal variation. The refractive index of the material within the container 64 varies in accordance with the pressure of the material. Accordingly, there are produced by means of the standing wave represented at 19 what, in effect, are cylindrical lenses such as 8l. Each of the cylindrical lenses functions to focus the light impinging thereon, derived from the kinescope and transmitted thereto through the transparent window E5, onto one of the color filter striations such as 61, E8 and 69.

There is impressed upon the crystal 15 a voltr age of one polarity having a stepped waveform such as shown at 82. There also is impressed upon the crystal 16 a similar voltage of opposite phase such as represented at 83. As a consequence, the inner or free faces of the crystals 15 and '16 are caused to move simultaneously in opposite directions and by substantially equal amounts. The movement of the inner face of the crystal 15 also causes a similar movement of the entire body of the exciting crystal 11. Inasmuch as the inner faces of the crystals 15 and 16 are moved in the :manner described, the distance between the inner face of the exciting crystal 11 and the inner or reflecting face of the crystal 16 remains substantially constant and the effect is to shift the standing wave pattern laterally relative to the colored filter striations such as 61, 6B, and 69.

To further explain the manner in which vthe color filter device, in .accordance with .this invention, operates to effect the reproduction oi' television images substantially in their natural colors, reference will be made to the fragmentary diagrammatic illustrations of Figures 5, 6, and 7. In Figure 5 is shown the position of the standing wave when the crystals 'L and 'H3 are energized respectively by voltages having the relative magnitudes shown by the steps 35i and of the voltage waves S2 and 83. The incident image-representative white light which impinges upon the effective cylindrical lenses such as Sii and 81 is refracted and focused substantially onto the red light transmitting striations such as 61 and 61 of the color filter. t will be understood that the light impinging upon all others of the effective cylindrical lenses is similarly focused onto red portions of the filter. It will be seen that there is substantially no loss of light except that relatively small portion which is absorbed in transmission through the filter device. Consequently, all of the light collected from the kinescope screen and caused to impinge upon the filter device is directed through the red light transmitting sections.

In Figure 6 are indicated the positions of the` effective cylindrical lenses 35 and 51 relative to the Acolor filter screen when voltages having the relative magnitudes indi-cated by the steps 88 and 89 of the voltage waves 82 and t3 are respectively impressed upon the crystals "i5 and l5. It will be observed that the effective lenses 86 and 8l have been moved far enough to the right as viewed in the drawing to cause the focussing of the incident white light impinging thereon through the green light transmitting sections such as 68 and 68 of the color filter.

Similarly, Figure 7 graphically illustrates the positions of the effective cylindrical lenses 8B and 81 relative to the filter screen when the crystals 15 and 1E are further distorted under the control of voltages such as represented by the steps SI and 92 of the voltage waves S2 and 83, respectively. ln these positions, it will be seen that the lenses 36 and 81 are effective to focus the incident white light onto the blue light transmitting sections such as G9 and Gd of the color lter screen.

It will be understood that, at the next succeeding instant, the described cycle of operation is repeated by suitable energization of the crystals 15 and 16 to shift the effective cylindrical lenses back to the positions shown in Figure 5.

A presently preferred method of forming the striated color filter` screen utilizes the standing waves produced in the device much in the same manner as they are employed in actual operation. rThis method comprises the employment of lphotographic techniques, the first step of which is to apply a coating of a ine grain photographic emulsion to the exterior surface of the transparent side wall G6. The exciting crystal 'il is suitably energized in the manner described to set up the standing waves forming the effective cylindrical lenses. Steady unidirectional voltages are applied to the crystals 15 and l having respective magnitudes corresponding, for example, to the steps .Bil and 85 of the voltage waves 82 and 83. Light, which may be substantially white, for example, is then directed through the transparent window 55 onto the effective cylindrical lenses which, under the conditions described, effect the concentration of this light into striations corresponding, for example, to the strips such as 61. Instead of white light, blue or ultra-light vmay vbe used, particularly if the emulsion is more sensitive to such light. Consequently, corresponding strips of emulsion are exposed to light so that upon subsequent development of the emulsion, there will be produced a bar structure comprising reduced silver. The silver images of the light bars are then converted to a silver-cyanide complex which serves as a mordant for an acid dye. Alternatively, a soft gelatine emulsion may be light sensitized with a chromate exposed to the light, after which the unexposed portions of the emulsion may be washed away. The remaining tanned images of the light bars may then be colored with an acid dye. In either case, the bar structure produced is dyed a particular color such as red, for example.

Then, the portions of the exterior surface of the transparent side wall B disposed between the red bars or striations are again -coated with a photographic emulsion. The crystals 'l5 and 'l5 then are energized by steady unidirectional voltages having magnitudes such as represented by the steps 88 and 89 of the voltage waves 32 and 83. In accordance with the operation of the device previously described, the standing waves forming the effective cylindrical lenses are shifted toward the right substantially into the position shown in Figure 6. The emulsion is then exposed to light directed thereto by the effective cylindrical lenses so that the portions of the emulsion positioned substantially in correspondence with the striations such as 68 are exposed to light. The previously-described process is repeated except that in this case the bars are dyed green.

Finally, the described process is again repeated with the crystals 'l5 and 16 energized by unidirectional voltages having magnitudes such as represented by the steps 9i and 92, respectively, of the voltage waves 82 and 83. The emulsion coating on the remaining portions of the exterior surface of the transparent side wall 66 are then exposed to light and dyed blue.

It will be seen that, by reason of the employment of the described process in the formation of the striated color lter screen under substantially the same conditions occurring in the operation of the device, very accurate registry of the light focussed by the effective cylindrical lenses with the respective differently colored striations of the color filter is effected.

In order for a color filter device of the character described to operate satisfactorily, it is necessary that the effective cylindrical lenses formed by the standing waves be capable of focussing the light in such a manner that, in the plane of the color lter screen, the light striations have widths substantially equal to one-half the distance by which adjacent edges of successive light strips are separated. This requirement may be satisfactorily met by suitably controlling the excitation of the material with which the container 54 is filled by means of the crystal 7l. The particular excitation required in any given case depends essentially upon the character of the medium in which the standing waves are to be produced. In general, the amplitude of the voltage by which the crystal 'il is excited is inversely proportional to the width of the light line produced in the plane of the color filter section. This is a result of the fact that an increase in the amplitude of excitation causes an increase in the pressure produced by the standing Waves and the fact that an increase in the pressure causes an increase in the index of refraction of the medium in the region of the standing waves.

An increase in the index of refraction produces an increase in the concentration of light or, in other words, the light is focussed into a smaller area. It will be seen, therefore, that by suitable adjustment of the excitation of the crystal 'l1 a striated light pattern of the desired form may be produced.

In View of the fact that the color filter device in accordance with this invention is interposed in the light path in such a manner that it is completely out of focus, the number of striations of which the filter device consists theoretically is immaterial. The picture resolution is, in no way, dependent upon the number of filter striations. However, in order to minimize the distance through which the standing waves have to be shifted for color selecting purposes and, consequently, to minimize the necessary distortion of the inner or free faces of the crystals 'l5 and '16, it is desirable to provide a substantial number of color lter striations. Accordingly, it has been determined that in a practical embodiment of the invention approximately striations per inch provides a suitable structure. It, therefore, is necessary to shift the standing waves by no more than approximately 3/100 of an inch to effect color selection in a three color system.

It is necessary, of course, to set up within the medium filling the container 64 standing waves of such a character that there is provided an effective cylindrical lens for each group of three color filter striations. This may be effected by a suitable choice of the frequency of the voltage by which the crystal Tl is excited. The number of eective cylindrical lenses which are produced by the standing waves is a function not only of the frequency of the voltage by which the crystal 'Il is excited but also of the velocity factor or rate of Wave propagation of the medium within the container 64.

There also are minimum requirements regarding the relationship between the frequency of the voltage by which the crystal 'Il is excited and the stepped wave voltages by which the crystals 15 and 'I6 are excited. In a three color television system, for example, it is necessary that the exciting voltage for the crystal 'l1 have a frequency which is at least three times the frequency at which the energization of the crystals 15 and 16 is varied. Accordingly, the crystals may be ground to such sizes that the crystal Tl has a resonant frequency which is at least three times the resonant frequency of the crystals 'I5 and 15.

Where a color filter device of the character described is to be used in a color television system of the dot multiplex type, the frequency at which the crystals 15 and 'I6 are required to operate is relatively high, corresponding to three times (in a three color system) the elemental or dot scanning frequency. It is seen that to grind a crystal for use as the exciting crystal 'll so that it has a resonant frequency which is effectively nine times the elemental or dot scanning frequency would result in an extremely thin structure. It has been determined, however, that satisfactory performance of a device of this character may be secured by exciting the crystal 11 at an odd harmonic of its fundamental or resonant frequency. In the case where the crystal Tl is excited at its third harmonic frequency, for example, it will be seen that in order to meet the requirements described, it may be of substantially the same size as the crystals l5 and 16.

11' A structure of this character is preferred for the additional reason that three identical crystals may be used.

Reference is made now to Figures 8, 9 and 10 for disclosure of typical examples of certain of the circuit components which may be employed in the illustrative embodiment of the invention. Initially, reference will be made particularly to Figure 8 wherein there are illustrated some of the details of a typical keying voltage source such as indicated generally at 3l of Figure 'l and at B3 of Figure 2. This portion of the keying voltage source of Figure 8 is commonly known as a ring multivibrator. It consists of as many multivibrator units as there are color components of the image to be reproduced. In the present instance, wherein it is assumed that the invention is embodied in a three color system, the keying voltage source consists of three multivibrator units S3, 94 and 95. The circuit details of each of these multivibrator units are substantially identical in the respective units and, consequently, only one such unit will be described particularly.

The multivibrator unit 93 includes a pair of electron tubes 96 and Sl; the multivibrator 94 includes electron tubes 98 and 99; and the multivibrator 95 includes electron tubes i3! and |52. The cathodes |93 and HM, respectively, of tubes 95 and ill are connected together and also to the respective suppressor grids |55 and ll, and are maintained at ground or other iixed potential. The anodes i lll and |08, respectively, of the tubes 95 and 91 are connected through individual load resistors E639 and respectively, and also through a common voltage-dropping resistor ||2 to the positive terminal oi a source of space current indicated at +B which also is bypassed to ground by a capacitor H3. The screen grids H4 and H5, respectively, of the tubes 96 and 91- are connected together and through a common voltage-dropping resistor H6 to the terminal -l-B. The anode |031 of the tube 96 is crosscoupled by means oi" a network including a parallel arrangement of a resistor il and a capacitor i8 to the control grid I9 of the tube 9i. Similarly, the anode |38 oi' the tube 91 is cross-coupled by means of a parallel arrangement of a resistor |20 and a capacitor |2| to the control grid |22 of the tube 36S. These cross-coupling arrangements are conventional in multivibrator practice and further description thereof is, accordingly, considered unnecessary. The control grids I9 and |22, respectively, of tubes 97 and 96 are suitably biased relative to their associated cathodes by means of the connection thereof through respective resistors |23 and |24 to a suitable source of negative biasing voltage indicated at -Bias The multivibrators Sd and 95 are .provided respectively with output terminals A-B, C-D and lil-F and also respectively with input terminals X, Y and Z. For controlling the timing of the operation ofthe ring multivibrator the input terminals are coupled to a source of a timing Wave such as the keying frequency oscillator 38 of Figure 1 or 63 of Figure For example, the input terminal X of the multivibrator 93 is coupled to the keying frequency oscillator by means of a circuit Which includes a series arrangement of a capacitor |25 and a unilaterally conducting device such as a crystal diode |26 and a shunt resistor |23. The diode |26 is connected in the circuit in such polarity that only the negative half cycles of the timing voltage wave, such as 62, are effective to control the operation of the ring multivibrator. Preferably, the parameters of the coupling circuit to the input terminals X, Y and Z of the ring multivibrators are so chosen that only the peaks of the negative half cycles of the voltage wave 62 are effective.

The output terminal B of the multivibrator f3 is coupled by a capacitor |28 to the input terminal Y of the multivibrator ilfl. Similarly, the output terminal D of the multivibrator is coupled by a capacitor |29 to the input terminal Z of the multivibrator 95, In like manner, the output terminal F of multivibrator S35 is coupled by a capacitor |3| to the input terminal X cf multivibrator 93. For the purpose ci deriving one oi the stepped voltage waves such as 5i! of Figure 2 for use in connection with the present invention, the voltage developed at the output terminals C and F of multivibrators fill and respectively are utilized` The manner in which the ring multivibrator of Figure 8 operates to generate the individual voltages which may be suitably combined to produce the required stepped voltage Waves 35 and 35 or" Figure l or 53 and 59 of Figure 2 will be described With additional reference to Figure 9. In this ligure, the waveforms |32 to |3'|y represent respectively the voltages developed at the multivibrator output terminals A to F. The wave |33 represents the sinusoidal voltage output derived from the keying frequency oscillator (S3 of Figure 2. A cycle of operation will be assumed to start at a time at which the tubes 91, 98, and ill! are conducting and the tubes Qt, 99 and |2 are nonconducting. At this time, the voltage developed at the output terminal B has a minimum positive magnitude as indicated at |39 of curve |33 and the voltage developed at the output terminal A has a maximum positive magnitude as indicated at M0 of curve |32. At the occurrence of the next succeeding negative peak if!! of the timing voltage Wave |38, there is impressed a negative voltage upon the input'terminals Ei, Y and Z. The impression of this negative voltage upon the control grids of the multivibrator tubes 99 and |32 is ineiective for the reason that these tubes are non-conducting. However, the impression of this negative voltage upon the control grid i3 of the tube Sil eiects the termination of space current conduction in this tube with the concomitant initiation of the conduction of space current in the tube 9&3 in accordance with well known multivibrator operation. Consequently, there is developed a voltage at the output terminal B of the multivibrator 93 which is of increased positive magnitude as indicated by the curve |33 so that, by means of the coupling capacitor |28, a positive voltage is impressed upon the input circuit of the tube Sil of the multivibrator 94. As a result, conduction oi space current is initiated in this tube and is terminated in the companion tube 98. The voltage developed at the output terminal C', therefore, increases to a positive maximum as indicated at M2 of the curve E34 and the voltage developed at the output terminal D decreases to a .positive minimum as indicated at M3 of the curve |35.

The next succeeding negative peak |44 of the timing wave |38 is ineffective to control tubes Sl and |02 but is effective to terminate the conduction of space current in the tube 99, whereupon the conduction of space current in the tube 98 is again initiated. The increased positive voltage developed at the output terminal D of the multivibrator 94, as indicated by the curve |35, when impressed by the coupling capacitor |29 upon the input circuit of the tube |02 of multivibrator 95 is effective to initiate the conduction of space current in this tube, as a result of which the conduction of space current in the tube I DI is terminated. Consequently, the voltage developed at the output terminal E increases to a positive maximum as indicated at |45 of the curve |36 and the voltage developed at the output terminal F decreases to a ypositive minimum as indicated at U36 of the curve |31.

The occurrence of the following negative peak M1 of the timing wave |38 is ineffective to control tubes 91 and S9, but effects the termination of the conduction of space current in the tube E02 which is effective to again initiate the conduction of space current in the tube IUI. The voltage developed at the output terminal F increases to a positive maximum as indicated by the curve |31 which, when impressed by the coupling capacitor i3| upon the input circuit of the tube 91 of multivibrator 93, again initiates the conduction of space current in this tube. The described cycle of operation then is repeated.

The voltage represented by the curves |36 and |31, derived respectively from the output terminals C and F of the ring multivibrator of Figure 8 are combined by a keying voltage adder, forming another portion of the keying voltage source 31 of Figure l or iii of Figure 2, and shown in Figure l for the production of the stepped voltage wave 35 of Figure l or 58 of Figure 2. Referring now to Figure l0, the keying voltage adder includes electron tubes |48 and |69 which, by way of example, are shown as pentodes. The cathodes |5| and |52 and the associated suppressor grids |53 and |513 of the tubes |48 and MB, respectively, are connected together and through a self-biasing network comprising a parallel arrangement of a resistor i55 and a capacitor |56 to ground or other point of fixed reference potential. 'Ihe anodes |51 and |58, respectively, of the tubes Hi8 and it are connected together to the output circuit and through a common load resistor 59 to a suitable source of space current for the tubes indicated at +B. The screen grids |6| and i572, respectively, of the tubes M8 and MS are connected together and through a common voltage-dropping resistor |63 to the l-l-B terminal. The control grid i613 of the tube |48 is coupled to the output terminal C of the keying voltage source by a series capacitor |65 with which is associated a shunt-connected leak resistor itt. Similarly, the control grid |61 of the tube ift@ is coupled by a series capacitor |68 and a shunt-connected leak resistor |59 to the output terminal F of the keying voltage source- The keying voltage adder of Figure l0 operates substantially in the following manner. There is impressed upon the control grid ite of the tube M8 a voltage having the waveform illustrated by the curve i3d of Figure 9. Similarly, there is impressed upon the control grid |i5 of the tube ili a voltage having substantially the. waveform shown by the curve |31 of Figure 9. It will be noted that the voltage wave |34 has a maximum positive amplitude during a period of unit length and a minimum positive amplitude for two succeeding periods of unit lengths. Also, it will be seen that the voltage wave |31 has a minimum positive amplitude for a period having a unit length and a maximum positive amplitude for two succeeding periods of unit lengths. Also, by comparing the time relationship of the voltage waves |3li and 131, it will be seen that, during the periods indicated at |1| and |12, respectiveiy,

14 the voltage at the output terminal F is maximum while the voltage at the output terminal C is minimum.

Let it be assumed that, in response to the impression of minimum positive voltages upon the respective control grids of the adder tubes |48 and |49, the input circuit biasing of these tubes is of such a character that the tubes conduct space current of minimum magnitude. In some instances, it may be desirable to so bias these tubes that, under such conditions, conduction of space current therein is completely interrupted. Assume for the purpose of the present invention that the latter condition prevails. Accordingly, during the interval represented by 1| and |12 of the curves |34 and 31, space current is conducted in the tube M9 only. As a result of the voltage drop produced in the load resistor |59 by this space current, there is developed at the output terminal of the keying voltage adder a voltage of intermediate magnitude as represented by the step |13 of the curve l'i of Figure 9 representing the waveform of the output voltage derived from the adder.

In the next succeeding period the input voltage to the control grid |61 of the tube |133 remains unchanged as indicated at |15 of the curve |14, while the magnitude of the input voltage to the control grid |64 of the tube |48 is increased to a positive maximum as indicated at HS of the curve |34. As a result, space current also is conducted in the tube Hi8 having a magnitude which will be assumed to be equal to that of the space current conducted in the tube |49. An additional voltage drop is produced in the load resistor |59, thereby decreasing the amplitude of the voltage derived from the output terminal as represented at |11 of the curve |113.

In the next succeeding time interval the voltage impressed upon 'the control grid |85 of tube |48 decreases to a minimum as indicated at |18 of curve |34 and the voltage impressed upon the control grid |51 of tube ils also decreases to a minimum as indicated at 18 of curve |31. Consequently, the conduction of space current is interrupted in both of the adder tubes, thereby developing a voltage of maximum positive amplitude at the output terminal, as indicated at i8| of curve |14. The described cycle of operation is then repeated.

In order to develop the oppositely phased voltages Sii of Figure l and 59 of Figure 2, the respective keying voltagesources 31 and 6| also include additional voltage adder apparatus similar to that described with reference vto Figure l0. In this case, however, the control grids |613 and |61, respectively, of tubes |128 and iii!! are coupled to output treminals D and E of the ring multi-vibrator of Figure 8, whereby to add the voltages having the waveforms represented by the curves 35 and |36. In view of the foregoing description of the manner in which apparatus of the character shown in Figure 10 functions to produce a stepped wave voltage of the form represented by the curve |15 of Figure 9 by adding voltages represented by curves Itll and |31, it should be obvious, without further description, that similar apparatus will produce a stepped wave voltage of the form represented by the curve I 82 of Figure 9 by adding voltages represented by the curves |35 and |35.

It is to be understood that the improved color television system in accordance with the present invention is not necessarily limited for use with the specic apparatus shown and described herein. For example, one of the components of the system is a source of light representing, in black and White, the different color components of the image to be reproduced. Principally for convenience and simplicity herein such a source of light has been referred to as a cathode ray tube such as the usual kinescope popularly employed in television receivers. It will be apparent, however, that wherever it may be found to be more convenient or desirable, lother sources of image representative light such as a moving picture ilm, a source of unmodulated light used in conjunction with a light valve, for example, may be used in other embodiments of the invention. A light valve employed in conjunction with an independent source of white light may be found to have certain advantages for use in a color television system operating in accordance with the dot multiplex system such as that disclosed in the copending Evans application referred to. Systems of this character require relatively high frequency of color changes in view of which some types of cathode ray tubes may be found to impose limitations upon the successful operation of such systems by reason of the fact that the phosphors of which the luminescent screens of such tubes are made necessarily have certain iinite times of decay. Conceivably, this property of cathode ray tubes could limit the usefulness of the tubes in a system of the character embodying the present invention for the reason that any particular screen area may be excited to emit light representative of one color and at a succeeding later instant be required to produce light representative of a different color component of the image. Unless the phosphor has the property of decaying substantially completely within the time occurring between successive excitations thereof, it is seen that there will be objectionable color dilution effected. However, it is to be clearly understood that such a limitation exists only with respect to cathode ray tubes including luminescent screens made of phosphore having relatively long decay times.

lIhe improved color filter device in accordance with this invention also will be understood to be susceptible of excitation by suitable voltages having waveforms other than the sinusoidal waveform illustratively shown and described herein. In general, it will be apparent that the waveform of the voltage by which the transparent medium is excited for the production of standing pressure waves therein determines the configuration of the effective lenticular elements formed in the medium. For example, in the illustrative embodiment of the invention disclosed `herein the transparent medium is excited by a sinusoidal voltage whereby to produce substantially cylindrical lenticular elements in the transparent medium. If, instead of a voltage having such a waveform, the transparent medium is excited ,by one having a sawtooth Waveform, the lenticular elements also will have substantially sawtooth configurations. Furthermore, it is considered to be within the scope of the present invention to provide additional excitation of the transparent medium whereby to produce different forms of lenticular bodies within the transparent medium. For example, the medium may be additionally excited substantially at right angles 4to the illustratively disclosed excitation. Such a `mode of operation will enable the formation within the transparent medium of a two dimensional lenticular body.

It thus is apparent that the present invention has a number of advantages over systems and apparatus previously devised for the purpose of effecting image reproduction substantially in natural colors. One of the more important advantages of the present system is Ithat it lprovides a relatively simple arrangement which is completely non-mechanical for colored image reproduction. The system, therefore, is inherently fast in its operation, thereby rendering it easily adaptable for use in any of -the well known types of color television systems including,f the field or frame sequential, the line sequential and the dot multiplex systems. Furthermore, by virtue of the character of the color filter device in accordance with this invention and the manner in which it may be used, it may, if desired, be made relatively small, particularly when used in conjunction with a projection type of reproducing device. Also, the use of such a color filter device renders the conversion of an existing black and white image reproducing system to one capable of reproducing images substantially in their natural colors a relatively simple mattei'. It will also be seen that, when the color iilter device in accordance with lone of the features of this invention is made by the illustratively disclosed process in accordance with another feature of the invention, the diiferent color registrations are particularly good because the striations of the color filter device are produced by precisely the same means employed to selectively direct the white light therethrough in the operation of the device.

It will be understood that the nature of the invention may be ascertained from the foregoing disclosure of an illustrative embodiment thereof which is .typical of other modifications within the spirit of the invention, and the scope of the invention may ybe determined from the following claims.

What is claimed is:

l. A color television image reproducing system, comprising means for producing a plurality of black and white partial images representative respectively of a plurality of color components of an image to be reproduced, a color filter device located in the path of light from said imageproducing means, a transparent medium located in said light path between said image-producing means and said filter device, means for producing pressure waves in said medium, thereby forming a plurality of effective lenses in Said medium by which to focus said light upon a group of areas of said filter device capable of transmitting light of a predetermined one of said plurality of colors, and means for variably positioning said pressure waves concurrently with color changes of said partial images to focus said light upon a dierent group of areas of said filter device capable of transmitting light of different colors corresponding with the colors represented by said partial images.

2. A color television image reproducing system, comprising means for producing a plurality of black and white partial images representative respectively of a plurality of color components of an image to be reproduced, a striated color nlter device located in the path of light from said image-producing means, a transparent medium located in said light path between said imageproducing means and said lter device, means for exciting said medium to produce pressure waves therein, thereby forming a plurality of eiective lenses in said medium by which te focus said light upon striations of said lter device capable of transmitting light of a predetermined one of said plurality of colors, and means fOr variably positioning said pressure Waves concurrently with color changes of said partial images to focus said light upon different striations of said iilter device capable of transmitting light of different colors corresponding with the colors represented by said partial images.

3. A color television image reproducing system, comprising means for producing a-plurality of black and white partial images representative respectively of a plurality of color components of an image to be reproduced, a striated color lter device located in the path of light from said image-producing means, an acoustically rigid transparent medium located in said light path between said image-producing means and said filter device, means including a rst source of `Wave energy for producing pressure waves in said medium, thereby forming a plurality of eiective lenses in said medium by which to focus said light upon striations of said lter device capable of transmitting light of a predetermined one of said plurality or colors, and means including a second source of energy for variably positioning said pressure waves concurrently with color changes of said partial images to focus said light upon different striations of said filter device capable of transmitting light of different colors corresponding with the colors represented by said partial images.

4. A color television image reproducing system, comprising a cathode ray tube having a luminescent screen for producing a plurality of black and white partial images representative respectively of a plurality of color components of an image to be reproduced, a striated color filter device located in the path of light from said screen, an acoustically hard transparent medium located in said light path between said screen and said lter device, means including a source of exciting wave energy for producing standing pressure Waves in said medium, thereby forming a plurality of effective condensing lenses in said medium by which to focus said light upon striations of said filter device capable of transmitting light of a predetermined one of said plurality of colors, and means including a source of color-selecting Wave energy for variably positioning said pressure waves concurrently with color changes of said partial images to focus said light upon different striations of said lter device capable of transmitting light of different colors corresponding with the colors represented by said partial images.

5. A color television image reproducing system, comprising a cathode ray tube having a luminescent screen and means including an electron beam for producing a plurality of black and White partial images representative respectively of a plurality of color components of an image to be reproduced, a striated color filter device located in the path of light from said screen, an acoustically hard transparent medium located in said light path between said screen and said lter device, means including a source of sinusoidal wave energy for producing sinusoidal standing pressure waves in said medium, thereby forming a plurality of effective cylindrical lenses in said medium by Which to rfocus said light upon striations of said lter device capable of transmitting light of a predetermined one of said plurality of colors, and means including a source of stepped wave energy for variably positioning said standing Waves concurrently with color changes :18 of said partial images to focus said light upon different striations of said lter device capable of transmitting light of different colors corresponding With the colors represented by said partial images.

6. A color lilter device for use in conjunction With a source of image representative substantially white light in a color television image reproducing system, comprising a transparent medium located in the path of light from said source and lbeing susceptible of having pressure Waves produced therein, a striated translucent element located adjacent one side of said medium in said light path, said striations being capable respectively of transmitting light of different colors, an exciting vibratory device mounted adjacent said medium and energizable to produce pressure waves in said medium angularly oriented relative to said light path, and at least one additional vibratory device mounted adjacent said medium and energizable to variably position said pressure waves .in said medium, whereby to successively focus said White light onto differently colored light-transmitting striations of said translucent element.

7. A color lter device for use in conjunction with a source of image representative substantially white light in a color television image reproducing system, comprising an acoustically hard transparent medium located in the path of light from said source, a striated translucent element located on one side of said medium in said light path, said striations being arranged in successive groups with corresponding striations of said groups capable respectively of transmitting light of different colors, an exciting vibratory device mounted adjacent said medium and energizable to produce pressure waves in said medium substantially perpendicularly to said light path, and a. pair of additional vibratory devices mounted adjacent v,said medium and energizable to variably position said pressure Waves in said medium, whereby to successively focus said white light onto diierent corresponding striations of said translucent element.

y 8. A color lter device for use in conjunction with a source of image representative substantially White light in a color television image reproducing system, comprising an acoustically hard transparent medium located in the path of light from said source, a striated translucent element located in the path of light emerging from said medium, said striations being arranged in successive groups with corresponding striations of said groups capable respectively of transmitting light of different colors, an exciting vibratory device mounted adjacent one end of said medium parallel to the path of light through said medium and energizable to produce pressure waves in said medium, and a pair of additional vibratory devices mounted respectively adjacent said exciting device and the opposite end of said medium, said pair of additional devices dening a pressure wave propagation path in said medium in which to produce standing pressure Waves by which to focus white light entering said medium onto corresponding striations of said translucent element, saidpair of additional devices being energizable in opposite sense to variably position said standing waves in said medium, whereby to successively focus said white light onto diierent corresponding striations of said translucent element.

9. A color iilter device for use in conjunction with a source ofimage representative substantially white light in a color television image reproducing system, comprising an lacoustic'ally hard transparenft material, a transparent element located on one side of said material, va stri'ated 'translucent element llocated on the opposite side of said material, said striations being arranged Lin successive groups with correspondin-g striations of 'said groups capable respectively oftransmitting'light or different colors, an exciting electro-mechanical -vibratory device rmounted adjacent one of =a second `pair -fof opposite sides of fsaidvm'aterial andenergizable to produce'pressure waves 4in said material, Iand a 'pair of additional `electro-mechanical vibrator-y devices mounted 'respectively adjacent said second ipair ofcpposi-te 'sides of said materialon'efo'f said-pair of additional devices supporting said exciting crystal and the other of said pair of additional devices reflecting `said Ypressure -waves-itc produce standingpressure Waves in said material-by-vvhich to focus light entering said ltransparent elementontocorresponding striations of fsaid'translucent element, said pair of additional (devices being simultaneously energiZahle-in ropposite sen-se to -variab'ly position said standing Waves in said material, whereby to successively focus light entering lsaid transparent 4element -onto different corresponding striations 'of said translucent element.

1.0. vAf color ilter device ffor use in conjunction Witlia source of image `representative substantially White 4*light Jin a color "television image reproducingfsystem; comprising a container `filled with ran i 'acoustically I hard transparent material, 'one'r-ofialiirstpairof opposite walls of said container f havinglia 'transparent 4.area and :the .other of'said fwalis hla'vinga s'triated translucent area, said fstri'ations b'eing f-arranged in successive groups 'with oorreslpon'ding r`stri-ations of 'said groups icapable respectively of transmitting light of "different .colors, a piezo-electric exciting( crystl-mountediadjacent onelof 'a secondvpair-of opposite Wallsf'offsaid-container and energizable toiproduce pressure'waves in said material, and a pairof additional:pieza-electric crystalsmounted respectively adjacent said second pair-'of container wallaone zof'sa-idipair of crystalssupportingron one face :thereof :saidexciting crystal and the other: of'said -pair ofl crystals re'iiecting `said pressure'waves'fto' 'produce standing pressure waves Vin said lma-terial by 1which' to 'focus light yentering said 'transparent area` onto corresponding v-striations 'ofsai-d'translucent area, said pair f crystalsbeing 4simuitaneously distortablev -in opposite sense' toi variablyi position said standing Wavesin said container, whereby tolsuccessively vfocus lig-ht entering said transparent-'area onto 'differentcon respondingfstriations 'ofk said translucent area.

11. A color` '1i-iter .device forl use in conjunction with `a'sourcefofirnage representative substantiallywvhiteilight in a color televisionimage're producing system,v comprising'a container filled with an-acoustically hard transparent Iliquid,ione ofia first pairv of opposite substantially parallel Walls -ofsaid container havinga transparent-area andI the other of said walls'having a istriated translucent area,` said 'striations' having substantially identical dimensions and being arranged in successive-,groups #Wi-th' corresponding striations of l said :groups capable respectively of transmittinglight of dii-ferent colors, Ia piezo-electric 'exciting crystal'` mounted 'adjacent Aone fof:` a second pair of opposite substantially para-llelvval-lsof-said container and energizable' to Aproduce pressure waves Yin: said Iliquids," and a. .pair of similar piezoelectricV crystalsf mounted respectively f adjacent said second -pair roi Acontainer walls, :one of said pair ro'f :crystals supporting .on one face thereof said exciting crystal and the other of said pair of crystals reiiecting said rpressure -Waves to produce standing pressure waves in said liquid by which to focus light entering said transparent area onto corresponding striations of said translucent area, said Ipair of .crystals being simultaneously distortable in substantially equal magnitude -and in opposite (sense .to variably position said-standing Waves in saidcontainer, whereby'to successively focus light entering said transparent area onto different corresponding striations Aof said translucent area.

1-2. The method o'f making a striated :colorl iilterscreensaid iilter screen having striations capable respectivelyvof transmitting light of different colors, said :method `comprising the steps of (l) forming pressure Waves in a transparent medium, r(2) exposing atleast one striated area of a layer Vof photosensitive materia-l -to light through said pressure waves, (3) removing Athe unexposed portions of said material, (4) coloring the-exposed residual portion of said material a predetermined color, (5) Vmoving said pressure Waves in said-material, and repeating steps (2), (i3), (54) `and (5) with respect toI other vstriated vareas of said material, each timecoloring the exposed `residual portions of said photosensitive material a vdifferent color until all portions of said iilter screen are covered.

`l3. The method of -making a striated color filter-screen, said lter screen having a multiplicity of striations capable of transmitting light of different colors and arranged in successive groups oirecurrin'g color transmitting properties, said-'method comprising the steps of, l) forming pressure Waves in aftransparent'medium, (2) exposing a'pl-urality of striated areas or" a layer of photosens'itive vmaterial. to light `through said pressure Waves, (3) lremoving the-unexposed portionsof said material, (4) coloring the exposed residual portions of said'material a predetermined color,l (5) moving said pressure waves-in said medium, and repeating Steps'(2), (3), (4) and (5) Vwith respect to other pluralities of striated areas, each'time coloring the exposed residualV portions of' said photosensitive material a-dif'ferent -coloruntil all portions :of said lter screen are' covered.

14. The method of 'makingwawstriated color lter screen for use'in a color television system, said iilter screen-having aI multiplicity ofv Striations capable of-transmittinglig-ht'of different colors and arranged in successive groups of recurring color transmitting properties, said method 4comprising the 'steps of, (l) forming pressure Waves inatransparent'medium, (2) exposing'a selected-group of-striated areas of alayer of photosensitive material to'iight through said pressure waves, (3) removing the Aunexposedportions oi' 'said material, (4) coloring the exposed residual portions `of said-material a predeterminedcolor, (5)` moving said pressure waves-relative to said exposedportions of said materiaLa-nd repeating steps (2), (3), (4) ,and (5) Awith respect to other groupso striated areas, each time coloring 'theexposed residual portions `of said` photosensitive material ,a `different color until all portions Yofsaid iter screen are covered.

15. The method Aof making a'striated color iilterscreen'for usel in a color'television system, said rvfilter screen A'having a' vmultiplicity of Striations"l capable "or transmitting light of dierent colors and arranged: in-V successive groups of recurring color transmitting properties, said method comprising the steps of, (1) forming standing pressure Waves in a transparent medium, (2) exposing a selected group of striated areas of a layer of photosensitive material to light through said standing pressure Waves, (3) dissolving the unexp'osed portions of said material, (4) dyeing the exposed residual portions of said material a predetermined color, (5) moving said standing pressure Waves :along their path of propagation, and repeating steps (2), (3), (4) and (5) with respect to other groups of striated areas, each time dyeing the exposed residual portions of said photosensitive material a diierent color until all portions of said filter screen are covered.

16. The method of making a striated color ilter screen for use in a color television system, said lter screen having Ia multiplicity of stria.- tions capable of transmitting light of different colors and arranged in successive groups of recurring color transmitting properties, said method comprising the steps of, (1) forming standing pressure Waves in a transparent acoustically rigid medium, (2) exposing a selected group of striated areas lof a layer of photosensitive material to monochromatic light focussed References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,109,540 Leishman Mar. 1, 1938 2,350,892 Hewson June 6, 1944 2,493,200 Land Jan. 3, 1950 2,513,520 Rosenthal July 4, 1950 2,528,510 Goldmark Nov. 7, 1950 2,557,794 Kibler June 26, 1951 FOREIGN PATENTS Number Country Date 473,061 Great Britain Oct. 5, 1937 620,032 Great Britain Mar, 18, 1949 

